Catheter ablation device with impedance monitoring

A microwave catheter ablation device for delivery of energy to a selected region of tissue, the microwave catheter ablation device comprising:

• an electrical feedline;
• an antenna portion including a radiating antenna electrically connectable via the electrical feedline to a microwave generator and configured to generate an electromagnetic field comprising electromagnetic waves in a microwave energy spectrum able to ablate tissue in the selected region of tissue;
• an elongated catheter having a distal tip, an outer sheath and one or more orifices formed through the outer sheath in or adjacent to the antenna portion, wherein the outer sheath is configured to allow a flow of fluid along the catheter to exit through the one or more orifices;
• and
• an impedance monitoring system comprising first and second electrodes positioned along a length of the catheter at locations spaced apart from the distal tip, wherein the first and second electrodes are arranged respectively inside and outside the outer sheath and configured such that in use the impedance monitoring system applies an electrical signal to create an electric circuit incorporating an ionic conductivity path through the fluid between the first electrode and the second electrode via the one or more orifices and the impedance monitoring system measures the impedance of the ionic conductivity path;
• wherein the second electrode is separate to the radiating antenna.